[Boatanchors] Ceramics help? Yes, it's boatanchor-related.

[mikea]

Amateur radio leads into all manner of interesting side-topics,
including in this case needing to do some fairly high-precision ceramics
construction. I'm also a Really Cheap Bastard who's unwilling to pay as
much as the manufacturer wants for three small ceramic widgets if I can
make them myself. 

I refer the interested reader to
those parts of <http://mikea.ath.cx/tubepix/> that refer to the Jettron
socket, and in particular to the image of the insulating ceramic spacer
to be found at <http://mikea.ath.cx/tubepix/8791-socket-washer.jpg>.
(caution: 1,548,661 byte image)

Those spacers are geting pretty crumbly,and fell apart on me as I was
inspecting things. They are each 1/2" OD and 1/16" thick at their
widest, with a 5/16" long 5/16" diameter shoulder, drilled to pass a #6
screw. The manufacturer wants $167.50 for three of them. Yes, $56.00
each, pretty near, for each of those little yellowish pieces of molded
porcelain. The manufacturer's quote came as rather a surprise, though I
should have expected it: the socket costs something like $500 new.

The spacers are nothing special, just unglazed fired porcelain. I
have access to a porcelain kiln, and I have a drill press and bits
suitable for making molds. Now I need a low-shrinkage porcelain with
good insulating properties and reasonable mechanical properties. The
potential across that 1/16" shoulder will be about 1000 Volts, and it
will be under no more than 50 pounds compressive force from the nut and
washers. That's not a lot of force, and the flat washer spreads it out
evenly.

I'm thinking about machining the mold cavities from split plaster
blocks, using flat-bottomed Forstner (or Pforstner) bits, though wood
might well suffice. I see a fair (or perhaps even unfair) amount of
experimentation coming up.

I'm also thinking about getting a chunk of PTFE rod and finding a small
lathe. That may turn out to be less work and less expense overall. 

Comments? Suggestions? Advice? Pointers?

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin